1. Field
The present description relates generally to wireless communication and more specifically to feedback of channel quality information (CQI) in a wireless communication system.
2. Background
An orthogonal frequency division multiple access (OFDMA) system utilizes orthogonal frequency division multiplexing (OFDM). OFDM is a multi-carrier modulation technique that partitions the overall system bandwidth into multiple (N) orthogonal frequency subcarriers. These subcarriers may also be called tones, bins, and frequency channels. Each subcarrier is associated with a respective sub carrier that may be modulated with data. Up to N modulation symbols may be sent on the N total subcarriers in each OFDM symbol period. These modulation symbols are converted to the time-domain with an N-point inverse fast Fourier transform (IFFT) to generate a transformed symbol that contains N time-domain chips or samples.
In a frequency hopping communication system, data is transmitted on different frequency subcarriers during different time intervals, which may be referred to as “hop periods.” These frequency subcarriers may be provided by orthogonal frequency division multiplexing, other multi-carrier modulation techniques, or some other constructs. With frequency hopping, the data transmission hops from subcarrier to subcarrier in a pseudo-random manner. This hopping provides frequency diversity and allows the data transmission to better withstand deleterious path effects such as narrow-band interference, jamming, fading, and so on.
Feedback of Channel Quality Indicator (CQI), e.g. channel information in a MIMO system is generally more challenging than CQI feedback for SISO systems. For SISO users, the CQI is computed at the access terminal (AT), using pilots sent over a dedicated control or signaling channel (FL-CTRL) or a data channel (FL-data). The CQI is fedback using a dedicated resource of a reverse link signaling or control channel (RL-CTRL).
Existing CQI feedback schemes assume a CQI table with a deterministic mapping scheme between the quantized CQI values and the packet-formats that can be supported by the AT. However, future wireless systems will support ATs with different capabilities (laptops, low-cost cell-phones, PCs, PDAs etc). This provides a great range of CQI quantization possibilities and thus increases the complexity of the feedback required. Furthermore, the deployments of next-generation wireless systems can vary hot-spots, partially loaded systems, fully loaded systems etc. Further, the different access points may vary from being configured for SISO to MIMO operation. Each of the scenarios generally requires different gradations of CQI quantization, and this further increases the complexity of the CQI feedback.
Thus, there exists a need in the art for a system and/or a methodology to optimize CQI feedback for different scenarios while at the same time maintaining the possibility of supporting the different scenarios.